222 



Three causes may be assigned in explanation of the absence 

 of proportional correlation in the flux of these nitrogenous sub- 

 stances and of the plankton, all of which are operative, but in 

 varying effectiveness at different times and under different 

 conditions . 



In the first place, the plankton itself constitutes but a part 

 of the total organic nitrogen; how small a one the data at 

 hand do not determine. Barring out error arising from the 

 death of the plankton and from the solution of the products 

 of its decay which might take place during the interval 

 between the collection and analysis of the sample, we find in 

 the relative amounts of albuminoid ammonia and total organic 

 nitrogen in solution and in suspension respectively some evi- 

 dence as to the possible limits of the proportionate amount which 

 the plankton and silt together form of the total nitrogenous 

 substances. The average amount ( Table X. ) of albuminoid 

 ammonia in solution and in suspension from July 6, 1897, to 

 March 28, 1899, is .355 and .131 parts per million respectively. 

 Plankton and silt together thus constitute about one third of 

 the total albuminoid ammonia in the Illinois River. The rela- 

 tive amounts of dissolved and suspended albuminoid ammonia at 

 the weekly intervals of analysis fluctuate according to access of 

 flood waters and increase in the plankton. The former is the 

 more potent factor. Usually the amount in suspension is from 

 one third to one half that in solution, rarely equaling or surpas- 

 sing it, as in the flood of February, 1898, when it rose to .4 as 

 compared with .28 in solution. The plankton pulse of April-May, 

 1898, accompanies a rise in total albuminoid ammonia from .4 

 to .6 — an increase of 50 per cent. The increase lies almost 

 entirely in the suspended form, which rises from a previous 

 level of .04 to .08, to .08 to .20, that is, it is more than doubled. 

 The volumetric increase in the plankton is, however, over 

 thirty-five-fold. Thus, under the most favorable conditions, 

 receding flood, little silt, and plankton maximum, the increase 

 in suspended albuminoid ammonia attending a thirty-five-fold 

 increase in the plankton constitutes but 33 per cent, of the total 



